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Brant Peppley Director Queen’s-RMC Fuel Cell Research Centre

Electrons, ions, heat, and fluids: The complex interplay of properties in porous electrodes and the porous transport layer. Brant Peppley Director Queen’s-RMC Fuel Cell Research Centre. CANADIAN TEAM Queen’s-RMC Fuel Cell Research Centre NRC-IFCI, Vancouver Group University of Victoria

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Brant Peppley Director Queen’s-RMC Fuel Cell Research Centre

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  1. Electrons, ions, heat, and fluids: The complex interplay of properties in porous electrodes and the porous transport layer Brant Peppley Director Queen’s-RMC Fuel Cell Research Centre • CANADIAN TEAM • Queen’s-RMC Fuel Cell Research CentreNRC-IFCI, Vancouver GroupUniversity of Victoria • Kunal Karan Michael Eikerling  Ned Djilali •  Jon Pharoah  John Stockie  Marc Secanell •  Brant Peppley • Univ of Waterloo Univ British Columbia NRC-ICPET, Ottawa Group • Michael Fowler Fariborz Taghipour  Steven Beale •  Sumit Kundu

  2. Electrons, ions, heat, and fluids: The complex interplay of properties in porous electrodes and the porous transport layer Brant Peppley Director Queen’s-RMC Fuel Cell Research Centre

  3. Macro-water management in PEM fuel cell e e e e e e + + + + + + + + Flooded + + Water Water Hydrogen Hydrogen water content + + Oxygen Oxygen membrane catalyst porous transport layer Dry

  4. Processes, Operating Parameters and Effects PEFC Key Sub-Components Catalyst Layer Species Transport & Electrochemical Kinetics Interface Properties • Overall • Performance • V-I Curves • Water Transport Composition Gas Diffusion Media Microstructure Bulk Properties • Operating Conditions • P, T, PO2, PH2, RH, Stoich Ratio Flow-Field Configuration

  5. Need for Gas Diffusion Media Optimisation+Considerations of 2-D and 3-D Effects

  6. 2-D Effects: Current Density Distributions Land Channel GDL Catalyst Layer Sun, W., Peppley, B.A.P. and Karan, K. (2005) Electrochimica Acta, 50 (16-17), 3359-3374. S. A. Freunberger et al. Electrochem. Comm. 8, (9), 2006, 1435-1438

  7. Carbon Paper is Inherently Anisotropic !!

  8. h=0.5V orthotropic orthotropic isotropic h=0.4V isotropic Land Channel GDL Catalyst Layer Influence of GDL Conductivity A A B B Isotropic In-plane conductivity = Through-plane conductivity Orthotropic In-plane conductivity = 10  (Through-plane conductivity)isotropic J.G. Pharoah, K. Karan, and W. Sun. (2006) J. Power Sources 161 (1), 214-224, 2006.

  9. 3D Effects: Straight Versus Serpentine Flow Fields

  10. 3D Effects – Influence of GDM Permeability Maximum current under the channel Location of maximum current varies with PTL permeability

  11. 3D Effects: Mass Transport/Convection in Channel and GDM • The flow in the channel is greatly reduced due to convection in the PTL • The secondary flow structures are greatly altered due to this mechanism • Very significant for • Transition to unsteady flow • Liquid transport

  12. 3D Effects: Water Accumulation in Serpentine Flow Channels Water is most often found in the bends! Neutron Imaging Data Courtesy of David Jacobsen, NIST

  13. FCRC Expertise/Capabilities T1 T2 q” • 2D and 3D Computational Fluid Dynamics (CFD) Calculations • Numerical Effective Transport Property Estimation Permeability EstimationEffective Conductivity Estimation (Lattice Boltzmann Method) Dan Hamilton, MSc Thesis, Queen’s University Mark Vandoormal, MSc Thesis, Queen’s University

  14. GDM Characterisation - FCRC Expertise/Capabilities (cont.) • Experimental Characterisation of GDM • Permeameter (Gas and Liquid Permeability) • Porometer (Hydrophobic and Hydrophilic Pores) • In-Situ Effective Permeability Measurement Brian Tysoe, MSc Thesis, Queen’s University

  15. CONCLUSION-1: GDM Can Strongly Affect FC Performance !!RECOMMENDATION-1:Proper Characterisation of GDM Transport and Physical Properties is Essential

  16. FC Sub-Components (geometry/material) Catalyst Layer Species Transport & Electrochemical Kinetics Interface Properties • Overall • Performance • V-I Curves • Water Transport Composition Gas Diffusion Media Microstructure Bulk Properties • Operating Conditions • P, T, PO2, PH2, RH, Stoich Ratio Flow-Field Configuration

  17. Need for Catalyst Layer Optimisation

  18. Cathode Agglomerate Model: Effectiveness Factor Land Channel GDL z Catalyst Layer x z Underutilized core of catalyst agglomerate x O2 diffusion path Sun, W., Peppley, B.A.P. and Karan, K. (2005) Electrochimica Acta, 50 (16-17), 3359-3374.

  19. Anode Agglomerate Model: Transport Limitations at Two-Scales Underutilized core of catalyst agglomerate ragg Only 40% of the outer core of the agglomerate is active Only 30% of the catalyst layer is utilized K. Karan (2007) Electrochem Comm. 9, 747-753; K. KaranStructural Modeling of PEMFC Anodes.211th ECS Meeting - Chicago, Illinois, May 6-11, 2007

  20. Catalyst Layer Optimisation M. Secanell, K. Karan, A. Suleman and N. Djilali (2007) Electrochimica Acta, 52, 22, 6318-6337.

  21. 3D Catalyst Layer Modeling

  22. Other Effects of Liquid Water in Catalyst Layer Slide title Electronically insulated agglomerate due to ionomer expansion (water intake) Ionically insulated agglomerate due to ionomer contraction (drying) Poor ionic conductivity due to imbalanced water drag and water back diffusion (anode) water drag water back diffusion Detection: decrease in ESA* decrease in ionic conductivity Detection: decrease in ESA* decrease in electronic conductivity Detection: little to none decrease in ESA* decrease in ionic conductivity Porous Transport Layer Catalyst Layer Membrane ionomer platinum particle (2-3 nm) carbon particle (~40 nm) secondary pore agglomerate (~ ?? nm, ~ particles) primary pore *ESA – electrochemically active surface area

  23. FCRC-NRC Capabilities • Microstructural Modeling • NRC-IFC • FCRC • CCL Optimisation • U. Victoria • Catalyst Layer Properties • FCRC • Catalyst Preparation • FCRC • NRC-IFCI

  24. Catalyst Layer Preparation Dimatix DMP2800 material printer Nafion-112 membrane 1 mm printed catalyst layer Fabrication of Catalyst Layer of Controlled Composition and Microstructure (?) 1 mm Carbon paper with microporous layer

  25. Electrochemically active surface area (ESA) measurement: cyclic voltammetry Slide title Potentiostat -2e- -1e- Pt + H2O PtO + 2H+ -SO3- + PtH -SO3H + Pt Nitrogen Nitrogen Hydrogen Hydrogen working electrode counter&reference electrode +1e- -SO3H + Pt -SO3- + PtH +2e- 2(-SO3H) 2(-SO3-) + H2

  26. Electronic conductivity of catalyst layer in PEM fuel cell Slide title platinum wires porous transport layer catalyst layer Teflon mesh membrane platinum wire

  27. Ionic conductivity of catalyst layer in PEM fuel cell Slide title oxygen gas phase diffusion ohmic resistance cathode charge transfer anode CPEC CPEA 0 RpA WC RpC Rohm Electrochemical Impedance Spectroscopy of PEM fuel cell porous transport layers membranes - = Catalyst layers

  28. CONCLUSION-2Transport and kinetics in catalyst layer strongly influence FC performance and water transport RECOMMENDATION-2Proper characterisation (microstructural and transport properties) and modeling of catalyst layer is key to optimising FC performance and water transport

  29. Micro-Porous Layer (MPL) as a Catalyst Layer-Gas Diffusion Media Interface:Need for MPL Optimisation

  30. PEMFC with Microporous Layers (MPLs) 200mm 1mm Porous Transport Layer (PTL) (gas diffusion layer) Catalyst Coated Membrane (CCM) Proton Exchange Membrane (PEM) Not to scale 200mm catalyst layer porous carbon backing microporous layer

  31. Role of MPL on Water Transport: Two Schools of Thoughts + + + + Cathode CL Porous Carbon Backing MPL Anode CL Membrane water drag with proton + + Water water back diffusion MPL helps remove water from Cathode CL to Cathode GDM MPL retains liquid water in Cathode CL and aids back diffusion • A.Z. Weber, J. Newman, J. Electrochem. Soc., 152 (2005) A677-A688. • G. Lin, T.V. Nguyen, J. Electrochem. Soc., 153 (2006) A372-A382. • J.H. Nam, M. Kaviany, Int. J. Heat Mass Transfer, 46 (2003) 4595-4611. • U. Pasaogullari, C.-Y. Wang, Electrochim. Acta, 49 (2004) 4359-4369.

  32. Effect of MPL on Water Drag H. K. Atiyeh, K. Karan, B. Peppley, A. Phoenix, E. Halliop and J. Pharoah (2007) J. of Power Sources, 170, 1, 111-K. Karan, H. Atiyeh, E. Halliop, A. Phoenix, B. Peppley, J. Pharoah, (2007) Electrochem Solid State Lett. 10, 2, B34-B38.

  33. Effect of MPL on Electrochemical Perfomance & Durability Cells with no MPLs Cells with MPL on at least one side H. K. Atiyeh, K. Karan, B. Peppley, A. Phoenix, E. Halliop and J. Pharoah (2007) J. of Power Sources, 170, 1, 111 K. Karan, H. Atiyeh, E. Halliop, A. Phoenix, B. Peppley, J. Pharoah, (2007) Electrochem Solid State Lett. 10, 2, B34

  34. MPL Reduces Fluoride Release Rate !! Thinned Membrane !! MPL on anode only MPL on cathode and anode S. Kundu, K. Karan, M. Fowler, L C Simon, B A Peppley, and E. Halliop, (Accepted Nov 2007). Influence of Micro-porous Layer and Operating Conditions on the Fluoride Release Rate and Degradation of PEMFC Membrane Electrode Assemblies, Journal of Power Sources.

  35. Single Cell Impedance Response – With and Without MPL Impedance diagrams for PEMFC with (2,3) and without (1) MPL fed with H2/Air (1,2) and H2/(20%O2 in He) (3). Current density – 0.21 A cm-2.

  36. Impedance Modeling Example: Porous SOFC Cathode (LSM/YSZ) Step 1. Step 2. Step 3. Step 4.

  37. Impedance Model – Comparison with Experimental Data

  38. Gas Diffusivity Effect Surface Diffusivity Effect Absorption/Desorption Rate Constant Effect

  39. CONCLUSION-3 Interfaces and interfacial layers (MPL) play a crucial role in water transport MPL can reduce membrane degradation !! Impedance modeling can help identify MPL’s role in water transportRECOMMENDATION-3 Proper characterisation (microstructural and transport properties) and modeling of MPL effects is important Optimisation of MPL is required for – improved water management – reduced membrane degradation

  40. Project partners & their tasks • Novel GDL,MPL • Surface properties (ESEM) • Application to stacks • Free surface flow in GDL/BPP • Robust design optimization • Microfluidic ex-situ experiments • Modeling at cell level • Mixed wettability characterization (exp.) • Structure property relation CL, MPL • Neutron imaging • Two-phase catalyst layer modeling, Interface conditions • Microstructural Catalyst Layer Modeling • 2D and 3D CFD Modeling of Half and Unit Cells • Numerical & Experimental Characterization of GDL and CL Properties • Impedance Characterizarion – Experimental & Simulation • MPL Characterisation • Mathematical Optimisation (Collaboration with UVic)

  41. Network of collaboration • Surface data (ESEM) • Modified GDLs, MPLs • Optimized design (GDL,BPP) • Surface modified BPPs (plasma etching) Free surface model GDL/channel GDL wettability data Interface conditions NI analysis • stacks incl. novel GDL&BPP • re-structured GDLs GDL wettability data Interface conditions NI analysis MPL/CL properties • GDL/MPL/CL Property Characterisation (Numerical & Simulation) • CL Modeling • Impedance Characterisation and Modeling • Mathematical Optimisation

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